The principles of the present invention are applicable to SELF-SCAN panels of the type shown and described in patents and applications cited below, and particularly, to SELF-SCAN panels of the type described and claimed in copending application Ser. No. 551,359, filed Feb. 20, 1975. The panels described therein are relatively simple in construction and operation; however, a problem sometimes arises in initiating a scanning cycle in which the columns of cathodes are scanned one by one. The present invention solves this problem.